1. Field of the Invention
The present invention relates to a door unlocking system and a door unlocking method and, more particularly, relates to a door unlocking system and a door unlocking method for unlocking a door of a vehicle through a wireless communication between an electronic key carried by a user and an in-vehicle device.
2. Description of the Related Art
A keyless entry system is known that unlocks a door of a vehicle through a wireless communication between an electronic key (portable device) carried by a user and an in-vehicle device. The electronic key has a built-in battery used as a power source for executing the wireless communication and a signal process with the vehicle. However, since the wireless communication and the signal process can no longer be executed if the battery of the electronic key loses all charge and dies, the electronic key is normally provided with a mechanical key (mechanical key) in preparation therefor.
In this regard, for example, JP 2007-297774 A discloses a system to which a communication system (a system utilizing a transponder activated by an activating radio wave) different from the keyless entry system is added so that this communication system is used in case of the battery losing all charge. This system enables locking/unlocking of a door without using the mechanical key when the battery of the electronic key losing all charge.
However, the locking/unlocking of a door is performed by using individual identification information of a transponder itself and this individual identification information is relatively simple, resulting in a problem that security is not as high as the keyless entry system.